Merge pull request #19306 from graydon/one-determined-heart

[Stats] Add SWIFTC_MAXIMUM_DETERMINISM to inhibit parallelism everywhere.

Author: graydon

include/swift/AST/DiagnosticsCommon.def

@@ -17,8 +17,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if !(defined(DIAG) || (defined(ERROR) && defined(WARNING) && defined(NOTE)))
-#  error Must define either DIAG or the set {ERROR,WARNING,NOTE}
+#if !(defined(DIAG) || (defined(ERROR) && defined(WARNING) && defined(NOTE) && defined(REMARK)))
+#  error Must define either DIAG or the set {ERROR,WARNING,NOTE,REMARK}
 #endif
 
 #ifndef ERROR
@@ -36,6 +36,11 @@
   DIAG(NOTE,ID,Options,Text,Signature)
 #endif
 
+#ifndef REMARK
+#  define REMARK(ID,Options,Text,Signature) \
+  DIAG(REMARK,ID,Options,Text,Signature)
+#endif
+
 ERROR(invalid_diagnostic,none,
       "INTERNAL ERROR: this diagnostic should not be produced", ())
 
@@ -58,6 +63,9 @@ NOTE(brace_stmt_suggest_do,none,
 NOTE(while_parsing_as_left_angle_bracket,none,
      "while parsing this '<' as a type parameter bracket", ())
 
+// Generic determinism-forcing override.
+REMARK(remark_max_determinism_overriding,none,
+         "SWIFTC_MAXIMUM_DETERMINISM overriding %0", (StringRef))
 
 // FIXME: This is used both as a parse error (a literal "super" outside a
 // method) and a type-checker error ("super" in a method of a non-class type).

include/swift/Basic/Statistic.h

@@ -68,6 +68,16 @@ class SourceManager;
 class Stmt;
 class TypeRepr;
 
+// There are a handful of cases where the swift compiler can introduce
+// counter-measurement noise via nondeterminism, especially via
+// parallelism; inhibiting all such cases reliably using existing avenues
+// is a bit tricky and depends both on delicate build-setting management
+// and some build-system support that is still pending (see
+// rdar://39528362); in the meantime we support an environment variable
+// ourselves to request blanket suppression of parallelism (and anything
+// else nondeterministic we find).
+bool environmentVariableRequestedMaximumDeterminism();
+
 class UnifiedStatsReporter {
 
 public:

lib/Basic/Statistic.cpp

@@ -50,6 +50,12 @@ namespace swift {
 using namespace llvm;
 using namespace llvm::sys;
 
+bool environmentVariableRequestedMaximumDeterminism() {
+  if (const char *S = ::getenv("SWIFTC_MAXIMUM_DETERMINISM"))
+    return (S[0] != '\0');
+  return false;
+}
+
 static int64_t
 getChildrenMaxResidentSetSize() {
 #if defined(HAVE_GETRUSAGE) && !defined(__HAIKU__)

lib/Driver/Driver.cpp

@@ -297,6 +297,11 @@ std::unique_ptr<sys::TaskQueue> Driver::buildTaskQueue(const Compilation &C) {
       return nullptr;
     }
   }
+  if (environmentVariableRequestedMaximumDeterminism()) {
+      NumberOfParallelCommands = 1;
+      Diags.diagnose(SourceLoc(), diag::remark_max_determinism_overriding,
+                     "-j");
+  }
 
   const bool DriverSkipExecution =
     ArgList.hasArg(options::OPT_driver_skip_execution,

lib/Frontend/CompilerInvocation.cpp

@@ -614,8 +614,13 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
                      A->getAsString(Args), A->getValue());
       return true;
     }
+    if (environmentVariableRequestedMaximumDeterminism()) {
+      Opts.NumThreads = 1;
+      Diags.diagnose(SourceLoc(), diag::remark_max_determinism_overriding,
+                     "-num-threads");
+    }
   }
-  
+
   if (Args.hasArg(OPT_sil_merge_partial_modules))
     Opts.MergePartialModules = true;
 

test/Misc/stats_max_determinism.swift

@@ -0,0 +1,6 @@
+// RUN: %empty-directory(%t)
+// RUN: env SWIFTC_MAXIMUM_DETERMINISM=1 %target-swiftc_driver -j 4 -num-threads 10 -c -o %t/out.o %s >%t/out.txt 2>&1
+// RUN: %FileCheck -input-file %t/out.txt %s
+// CHECK: remark: SWIFTC_MAXIMUM_DETERMINISM overriding -j
+// CHECK: remark: SWIFTC_MAXIMUM_DETERMINISM overriding -num-threads
+print(1)